The present invention relates to a water propulsion apparatus, and more generally, to a thrust generating oscillating fin propulsion apparatus adapted for underwater propulsion.
Pedal operated propulsion apparatus, such as a foot operated paddle boat described in U.S. Pat. No. 3,095,850, are known in the art. Other pedal operated means linking rotatable pedals to a propeller have been proposed. Some have looked to the swimming motion of sea creatures to design mechanically powered propulsion systems. Generally speaking, the swimming behavior of sea creatures may be classified into two distinct modes of motion: middle fin motion or median and paired fin (MPF) mode and tail fin or body and—caudal fin (BCF) mode, based upon the body structures involved in thrust production. Within each of these classifications, there are numerous swimming modes along a spectrum of behaviors from purely undulatory to entirely oscillatory modes. In undulatory swimming modes thrust is produced by wave-like movements of the propulsive structure (usually a fin or the whole body). Oscillatory modes, on the other hand, are characterized by thrust production from a swiveling of the propulsive structure at the attachment point without any wave-like motion. A penguin or a turtle, for example, may be considered to have movements generally consistent with an oscillatory mode of propulsion.
In 1997, Massachusetts Institute of Technology (MIT) researchers reported that a propulsion system that utilized two oscillating blades of MPF mode produced thrust by sweeping back and forth in opposite directions had achieved efficiencies of 87%, compared to 70% efficiencies for conventional watercraft. A 12-foot scale model of the MIT Proteus “penguin boat” was capable of moving as fast as conventional propeller driven watercraft. Another MIT propulsion system referred to as a “Robotuna,” utilized a tail in BCF mode propulsion patterned after a blue fin tuna, achieved efficiencies of 85%. Based upon limited studies, higher efficiencies of 87% (and by some reports 90-95% efficiency) may be possible with oscillatory MPF mode propulsion that may enable relatively long distances of human powered propulsion being achieved both on and under the water surface.
U.S. Pat. No. 6,022,249 describes a kayak having a propulsion system that extends below the water line. The propulsion system includes a pair of flappers in series, each adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of the kayak.